Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$166.37	11.423%	$185.3744	$185.37	$185.35	$185.40
Purchase #2	$56.52	5.863%	$59.8338	$59.83	$59.85	$59.80
Purchase #3	$216.54	6.356%	$230.3033	$230.30	$230.30	$230.30
Purchase #4	$188.80	6.199%	$200.5037	$200.50	$200.50	$200.50
Purchase #5	$240.72	13.842%	$274.0405	$274.04	$274.05	$274.00
Purchase #6	$165.68	6.734%	$176.8369	$176.84	$176.85	$176.80
Purchase #7	$146.54	4.779%	$153.5431	$153.54	$153.55	$153.50
7 purchase totals =	$1,181.17		$1,280.4357	$1,280.42	$1,280.45	$1,280.30